Novel silicone composition crosslinking catalysts

ABSTRACT

The invention relates to a crosslinkable composition X, comprising: at least one organopolysiloxane compound A comprising, per molecule, at least two C2-C6 alkenyl radicals bonded to silicon atoms; at least one organohydrogenopolysiloxane compound B comprising, per molecule, at least two hydrogen atoms bonded to an identical or different silicon atom; at least one catalyst C which is a complex corresponding to the following formula: [Fe(L1)2] in which: the symbol Fe represents iron at degree of oxidation II; the symbols L1, which may be identical or different, represent a ligand which is a β-dicarbonylato anion or the enolate anion of a β-dicarbonylated compound; optionally at least one adhesion promoter D; and optionally at least one charge E. The invention also relates to the use of the previously described catalyst C as silicone composition crosslinking catalyst, to a silicone composition crosslinking method, wherein it comprises heating the composition X to a temperature of between 70 and 200° C., and to the resulting crosslinked silicone material Y.

FIELD OF THE INVENTION

The present invention relates to the field of crosslinking of siliconecompositions, in which reagents bearing at least two unsaturated bondsand organosilicon compounds bearing at least two hydrogenosilyl units(—SiH) are placed in contact in the presence of a catalyst C which is acomplex corresponding to the following formula:

[Fe(L¹)₂]

-   -   in which:        -   the symbol Fe represents iron in oxidation state II,        -   the symbols L¹, which may be identical or different,            represent a ligand which is a β-dicarbonylato anion or the            enolate anion of a β-dicarbonyl compound.

TECHNICAL BACKGROUND

In the field of crosslinking of silicone compositions, hydrosilylation,also known as polyaddition, is a predominant reaction.

During a hydrosilylation reaction, a compound comprising at least oneunsaturation reacts with a compound comprising at least one hydrogenatom bonded to a silicon atom. This reaction may be described, forexample, by the reaction equation (1) in the case of an unsaturation ofalkene type:

or by the reaction equation (2) in the case of an unsaturation of alkynetype:

The hydrosilylation of unsaturated compounds is performed by catalysis,using an organometallic catalyst. Currently, the organometallic catalystthat is suitable for this reaction is a platinum catalyst. Thus, themajority of the industrial hydrosilylation reactions are catalyzed bythe platinum Karstedt complex, of general formulaPt₂(divinyltetramethyldisiloxane)₃ (abbreviated as Pt₂(DVTMS)₃):

At the start of the 2000s, the preparation of platinum-carbene complexesof general formula:

afforded access to more stable catalysts (see, for example,international patent application WO 01/42258).

However, the use of platinum organometallic catalysts is stillproblematic. It is a toxic, expensive metal that is becoming harder tofind, and the price of which fluctuates enormously. It is thereforedifficult to use at the industrial scale. It is thus desired to minimizethe amount of catalyst required for the reaction, without, however,reducing the yield or the reaction rate. Moreover, it is desired to haveavailable a catalyst that is stable over the course of the reaction. Ithas been found that, during the catalyzed reaction, platinum metal canprecipitate, leading to the formation of insoluble colloids in thereaction medium. The catalyst is then less active. Furthermore, thesecolloids form cloudiness in the reaction medium, and the productsobtained are not esthetically satisfying because they are colored.

Finally, platinum-based complexes catalyze hydrosilylation reactions atroom temperature with rapid kinetics, of the order of a few minutes. Inorder to have the time to prepare, transport and use the compositionbefore it has cured, it is often necessary to temporarily inhibit thehydrosilylation reaction. For example, when it is desired to coat apaper or polymer substrate with a nonstick silicone coat, the siliconecomposition is formulated to form a bath which must remain liquid atroom temperature for several hours before being deposited on thesubstrate. It is only after this deposition that it is desired for thecuring by hydrosilylation to take place. The introduction ofhydrosilylation-inhibiting additives makes it possible to efficientlyprevent the reaction for as long as necessary before activation.However, it is occasionally necessary to use large amounts of inhibitor,which causes strong inhibition of the hydrosilylation catalyst. As aconsequence, the rate of curing of the composition, even afteractivation, is slowed down, which is a major drawback from an industrialviewpoint since this especially makes it necessary to reduce the coatingrate and thus the production rate.

It would therefore be advantageous to propose alternative organometalliccatalysts to the platinum-based catalysts and to have available novelcompositions that are crosslinkable and/or curable by means of catalyststhat no longer have the problems described above, in particular that donot require the use of an inhibitor.

This objective is achieved with the aid of a catalyst which is an iron(II) complex having a specific structure. These catalysts, inparticular, do not need to be handled under a protective atmosphere (forexample under argon). The crosslinking reactions in which they are usedmay also be performed in the open air, without a protective atmosphere.

According to a first aspect, a subject of the present invention is thusa crosslinkable composition X comprising:

-   -   at least one organopolysiloxane compound A comprising, per        molecule, at least two C₂-C₆ alkenyl radicals bonded to silicon        atoms,    -   at least one organohydrogenopolysiloxane compound B comprising,        per molecule, at least two hydrogen atoms bonded to an identical        or different silicon atom,        -   at least one catalyst C which is a complex corresponding to            the following formula:

[Fe(L¹)₂]

-   -   in which:        -   the symbol Fe represents iron in oxidation state II,        -   the symbols L¹, which may be identical or different,            represent a ligand which is a β-dicarbonylato anion or the            enolate anion of a β-dicarbonyl compound,    -   optionally at least one adhesion promoter D and    -   optionally at least one filler E.

Composition X according to the invention is crosslinkable, i.e., for thepurposes of the present patent application, once the compounds A and Bhave reacted together in the presence of the catalyst C, athree-dimensional network forms, which leads to curing of thecomposition. Crosslinking thus involves a gradual physical change in themedium constituting the composition.

According to a second aspect, a subject of the invention is also the useof the catalyst C described previously as a catalyst for crosslinkingsilicone compositions.

According to a third aspect, a subject of the invention is also aprocess for crosslinking silicone compositions, characterized in that itconsists in heating composition X described previously to a temperatureranging from 70 to 200° C., preferably from 80 to 150° C. and morepreferentially from 80 to 130° C., and also the crosslinked siliconematerial Y thus obtained.

Finally, according to a fourth aspect, a subject of the invention is acrosslinked silicone material Y obtained by heating to a temperatureranging from 70 to 200° C., preferably from 80 to 150° C. and morepreferentially from 80 to 130° C., of a crosslinkable composition X asdescribed previously.

The term “crosslinked silicone material” means any silicone-basedproduct obtained by crosslinking and/or curing of compositionscomprising organopolysiloxanes bearing at least two unsaturated bondsand organopolysiloxanes bearing at least two hydrogenosilyl units(—SiH). The crosslinked silicone material may be, for example, anelastomer, a gel or a foam.

According to a particularly advantageous mode, the organopolysiloxane Acomprising, per molecule, at least two C₂-C₆ alkenyl radicals bonded tosilicon atoms, comprises:

-   -   (i) at least two siloxyl units (A.1), which may be identical or        different, having the following formula:

$\begin{matrix}{W_{a}Z_{b}{SiO}_{\frac{4 - {({a + b})}}{2}}} & \left( {A{.1}} \right)\end{matrix}$

-   -   -   in which:            -   a=1 or 2, b=0, 1 or 2 and a+b=1, 2 or 3;            -   the symbols W, which may be identical or different,                represent a linear or branched C₂-C₆ alkenyl group,            -   and the symbols Z, which may be identical or different,                represent a monovalent hydrocarbon-based group                containing from 1 to 30 carbon atoms, preferably chosen                from the group formed by alkyl groups containing from 1                to 8 carbon atoms and aryl groups containing between 6                and 12 carbon atoms, and even more preferentially chosen                from the group formed by methyl, ethyl, propyl,                3,3,3-trifluoropropyl, xylyl, tolyl and phenyl radicals,

    -   (ii) and optionally at least one siloxyl unit having the        following formula:

$\begin{matrix}{Z_{a}^{1}{SiO}_{\frac{4 - a}{2}}} & \left( {A{.2}} \right)\end{matrix}$

-   -   -   in which:            -   a=0, 1, 2 or 3,            -   the symbols Z¹, which may be identical or different,                represent a monovalent hydrocarbon-based group                containing from 1 to 30 carbon atoms, preferably chosen                from the group formed by alkyl groups containing from 1                to 8 carbon atoms inclusive and aryl groups containing                between 6 and 12 carbon atoms, and even more                preferentially chosen from the group formed by methyl,                ethyl, propyl, 3,3,3-trifluoropropyl, xylyl, tolyl and                phenyl radicals.

Advantageously, the radicals Z and Z¹ are chosen from the group formedby methyl and phenyl radicals, and W is chosen from the following list:vinyl, propenyl, 3-butenyl, 5-hexenyl, 9-decenyl, 10-undecenyl,5,9-decadienyl and 6-11-dodecadienyl, and preferably, W is a vinyl.

These organopolysiloxanes may have a linear, branched or cyclicstructure. Their degree of polymerization is preferably between 2 and5000.

When they are linear polymers, they are essentially formed from siloxylunits “D” chosen from the group formed by the siloxyl units W₂SiO_(2/2),WZSiO_(2/2) and Z¹ ₂SiO_(2/2), and from siloxyl units “M” chosen fromthe group formed by the siloxyl units W₃SiO_(1/2), WZ₂SiO_(1/2),W₂ZSiO_(1/2) and Z¹ ₃SiO_(1/2). The symbols W, Z and Z¹ are as describedabove.

As examples of end units “M”, mention may be made of trimethylsiloxy,dimethylphenylsiloxy, dimethylvinylsiloxy or dimethylhexenylsiloxygroups.

As examples of units “D”, mention may be made of dimethylsiloxy,methylphenylsiloxy, methylvinylsiloxy, methylbutenylsiloxy,methylhexenylsiloxy, methyldecenylsiloxy or methyldecadienylsiloxygroups.

Said organopolysiloxanes A may be oils with a dynamic viscosity fromabout 10 to 100 000 mPa·s at 25° C., generally from about 10 to 70 000mPa·s at 25° C., or gums with a molecular mass of about 1 000 000 mPa·sor more at 25° C.

All the viscosities under consideration in the present descriptioncorrespond to a “Newtonian” dynamic viscosity magnitude at 25° C., i.e.the dynamic viscosity which is measured, in a manner that is known perse, with a Brookfield viscometer at a shear rate gradient that is lowenough for the measured viscosity to be independent of the rategradient.

When they are cyclic organopolysiloxanes, they are formed from siloxylunits “D” having the following formulae: W₂SiO_(2/2), Z₂SiO_(2/2) orWZSiO_(2/2), which may be of the dialkylsiloxy, alkylarylsiloxy,alkylvinylsiloxy or alkylsiloxy type. Examples of such siloxyl unitshave already been mentioned above. Said cyclic organopolysiloxanes Ahave a viscosity from about 10 to 5000 mPa·s at 25° C.

According to a preferred embodiment, composition X according to theinvention comprises a second organopolysiloxane compound comprising, permolecule, at least two C₂-C₆ alkenyl radicals bonded to silicon atoms,different from the organopolysiloxane compound A, said secondorganopolysiloxane compound preferably being divinyltetramethyl siloxane(dvtms).

Preferably, the organopolysiloxane compound A has a mass content ofSi-vinyl units of between 0.001 and 30%, preferably between 0.01 and10%.

According to a preferred embodiment, the organohydrogenopolysiloxanecompound B is an organopolysiloxane containing at least two hydrogenatoms per molecule, bonded to an identical or different silicon atom,and preferably containing at least three hydrogen atoms per moleculedirectly bonded to an identical or different silicon atom.

Advantageously, the organohydrogenopolysiloxane compound B is anorganopolysiloxane comprising:

-   -   (i) at least two siloxyl units and preferably at least three        siloxyl units having the following formula:

$\begin{matrix}{H_{d}Z_{e}^{3}{SiO}_{\frac{4 - {({d + e})}}{2}}} & \left( {B{.1}} \right)\end{matrix}$

-   -   -   in which:            -   d=1 or 2, e=0, 1 or 2 and d+e=1, 2 or 3,            -   the symbols Z³, which may be identical or different,                represent a monovalent hydrocarbon-based group                containing from 1 to 30 carbon atoms, preferably chosen                from the group formed by alkyl groups containing from 1                to 8 carbon atoms and aryl groups containing between 6                and 12 carbon atoms, and even more preferentially chosen                from the group formed by methyl, ethyl, propyl,                3,3,3-trifluoropropyl, xylyl, tolyl and phenyl radicals,                and

    -   (ii) optionally at least one siloxyl unit having the following        formula:

$\begin{matrix}{Z_{c}^{2}{SiO}_{\frac{4 - c}{2}}} & \left( {B{.2}} \right)\end{matrix}$

-   -   -   in which:            -   c=0, 1, 2 or 3,            -   the symbols Z², which may be identical or different,                represent a monovalent hydrocarbon-based group                containing from 1 to 30 carbon atoms, preferably chosen                from the group formed by alkyl groups containing from 1                to 8 carbon atoms and aryl groups containing between 6                and 12 carbon atoms, and even more preferentially chosen                from the group formed by methyl, ethyl, propyl,                3,3,3-trifluoropropyl, xylyl, tolyl and phenyl radicals.

The organohydrogenopolysiloxane compound B may be formed solely fromsiloxyl units of formula (B.1) or may also comprise units of formula(B.2). It may have a linear, branched or cyclic structure. The degree ofpolymerization is preferably greater than or equal to 2. More generally,it is less than 5000.

Examples of siloxyl units of formula (B.1) are especially the followingunits: H(CH₃)₂SiO_(1/2), HCH₃SiO_(2/2) and H(C₆H₅)SiO_(2/2).

When they are linear polymers, they are essentially formed from:

-   -   siloxyl units “D” chosen from the units having the following        formulae Z² ₂SiO_(2/2) or Z³HSiO_(2/2), and    -   siloxyl units “M” chosen from the units having the following        formulae Z² ₃SiO_(1/2) or Z³ ₂HSiO_(1/2).

These linear organopolysiloxanes may be oils with a dynamic viscosityfrom about 1 to 100 000 mPa·s at 25° C., generally from about 10 to 5000mPa·s at 25° C., or gums with a molecular mass of about 1 000 000 mPa·sor more at 25° C.

When they are cyclic organopolysiloxanes, they are formed from siloxylunits “D” having the following formulae Z² ₂SiO_(2/2) and Z³HSiO_(2/2),which may be of the dialkylsiloxy or alkylarylsiloxy type or unitsZ³HSiO_(2/2) solely. They then have a viscosity from about 1 to 5000mPa·s.

Examples of linear organohydrogenopolysiloxane compounds B are:dimethylpolysiloxanes bearing hydrogenodimethylsilyl end groups,dimethylhydrogenomethylpolysiloxanes bearing trimethylsilyl end groups,dimethylhydrogenomethylpolysiloxanes bearing hydrogenodimethylsilyl endgroups, hydrogenomethylpolysiloxanes bearing trimethylsilyl end groups,and cyclic hydrogenomethylpolysiloxanes.

The oligomers and polymers corresponding to the general formula (B.3)are especially preferred as organohydrogenopolysiloxane compound B:

-   -   in which:        -   x and y are an integer ranging between 0 and 200,        -   the symbols R¹, which may be identical or different,            represent, independently of each other:            -   a linear or branched alkyl radical containing 1 to 8                carbon atoms, optionally substituted with at least one                halogen, preferably fluorine, the alkyl radicals                preferably being methyl, ethyl, propyl, octyl and                3,3,3-trifluoropropyl,            -   a cycloalkyl radical containing between 5 and 8 cyclic                carbon atoms,            -   an aryl radical containing between 6 and 12 carbon                atoms, or            -   an aralkyl radical bearing an alkyl part containing                between 5 and 14 carbon atoms and an aryl part                containing between 6 and 12 carbon atoms.

The following compounds are particularly suitable for the invention asorganohydrogenopolysiloxane compound B:

-   -   with a, b, c, d and e defined below:        -   in the polymer of formula S1:            -   0≤a≤150, preferably 0≤a≤100, and more particularly                0≤a≤20, and            -   1≤b≤90, preferably 10≤b≤80 and more particularly                30≤b≤70,    -   in the polymer of formula S2: 0≤c≤15        -   in the polymer of formula S3: 5≤d≤200, preferably 20≤d≤100,            and 2≤e≤90, preferably 10≤e≤70.

In particular, the organohydrogenopolysiloxane compound B that issuitable for use in the invention is the compound of formula S1, inwhich a=0.

Preferably, the organohydrogenopolysiloxane compound B has a masscontent of SiH units of between 0.2 and 91%, preferably between 0.2 and50%.

In the context of the invention, the proportions of theorganopolysiloxane A and of the organohydrogenopolysiloxane B are suchthat the mole ratio of the hydrogen atoms bonded to silicon (Si—H) inthe organohydrogenopolysiloxane B to the alkenyl radicals bonded tosilicon (Si—CH═CH₂) in the organopolysiloxane A is between 0.2 and 20,preferably between 0.5 and 15, more preferentially between 0.5 and 10and even more preferentially between 0.5 and 5.

According to a preferred embodiment, the organopolysiloxane A and/or theorganohydrogenopolysiloxane B may be degassed under an inert atmosphereof nitrogen (N₂) or argon (Ar) to promote the crosslinking.

The composition according to the invention uses at least one catalyst Cwhich is a complex corresponding to the following formula:

[Fe(L¹)₂]

-   -   in which:        -   the symbol Fe represents iron in oxidation state II,        -   the symbols L¹, which may be identical or different,            represent a ligand which is a β-dicarbonylato anion or the            enolate anion of a β-dicarbonyl compound.

It should be noted that at least part of the inventive nature of theinvention is due to the judicious and advantageous selection of thestructure of the catalyst C.

According to another preferred embodiment of the invention, the ligandL¹ is an anion derived from a compound of formula (1): R¹COCHR²COR³ (1)

in which:

-   -   R¹ and R³, which may be identical or different, represent a        linear, cyclic or branched C₁-C₃₀ hydrocarbon-based radical, an        aryl containing between 6 and 12 carbon atoms or a radical —OR⁴        with R⁴ representing a linear, cyclic or branched C₁-C₃₀        hydrocarbon-based radical,    -   R² is a hydrogen atom or a hydrocarbon-based radical, preferably        an alkyl radical comprising from 1 to 4 carbon atoms; with    -   R¹ and R² may be joined together to form a C₅-C₆ ring, and    -   R² and R⁴ may be joined together to form a C₅-C₆ ring.

Advantageously, the compound of formula (1) is chosen from the groupformed by the β-diketones: 2,4-pentanedione (acac); 2,4-hexanedione;2,4-heptanedione; 3,5-heptanedione; 3-ethyl-2,4-pentanedione;5-methyl-2,4-hexanedione; 2,4-octanedione; 3,5-octanedione;5,5-dimethyl-2,4-hexanedione; 6-methyl-2,4-heptanedione;2,2-dimethyl-3,5-nonanedione; 2,6-dimethyl-3,5-heptanedione;2-acetylcyclohexanone (Cy-acac); 2,2,6,6-tetramethyl-3,5-heptanedione(TMHD); 1,1,1,5,5,5-hexafluoro-2,4-pentanedione (F-acac);benzoylacetone; dibenzoylmethane; 3-methyl-2,4-pentadione;3-acetyl-2-pentanone; 3-acetyl-2-hexanone; 3-acetyl-2-heptanone;3-acetyl-5-methyl-2-hexanone; benzoylstearoylmethane;benzoylpalmitoylmethane; octanoylbenzoylmethane;4-t-butyl-4′-methoxydibenzoylmethane; 4,4′-dimethoxydibenzoylmethane and4,4′-di-tert-butyldibenzoylmethane, and preferably from the β-diketones2,4-pentanedione (acac) and 2,2,6,6-tetramethyl-3,5-heptanedione (TMHD).

According to another preferred embodiment of the invention, theβ-dicarbonylato ligand L¹ is a β-keto esterate anion chosen from thegroup formed by anions derived from the following compounds: methyl,ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, tert-butyl,isopentyl, n-hexyl, n-octyl, 1-methylheptyl, n-nonyl, n-decyl andn-dodecyl esters of acetylacetic acid or those described in patentapplication FR-A-1435882.

According to a particularly preferred embodiment, the catalyst C ischosen from the complexes [Fe(acac)₂] and [Fe(TMHD)₂]. It is understoodthat, in the above formulae, “acac” means the anion derived from thecompound 2,4-pentanedione and “TMHD” means the anion derived from thecompound 2,2,6,6-tetramethyl-3,5-heptanedione.

The catalyst C may especially be present in composition X according tothe invention in a content ranging from 0.001 to 10 mol % of iron pernumber of moles of C₂-C₆ alkenyl radicals bonded to silicon atoms in theorganopolysiloxane compound A, preferably from 0.01 to 7%, and morepreferentially from 0.1 to 5%.

Composition X according to the invention is preferably free of catalystbased on platinum, palladium, ruthenium or rhodium. The term “free” ofcatalyst other than the catalyst C means that composition X according tothe invention comprises less than 0.1% by weight of catalyst other thanthe catalyst C, preferably less than 0.01% by weight, and morepreferentially less than 0.001% by weight, relative to the total weightof the composition.

Composition X may advantageously comprise at least one adhesion promoterD.

-   -   Without this being limiting, it may be considered that the        adhesion promoter D comprises:        -   (D.1) at least one alkoxylated organosilane containing, per            molecule, at least one C₂-C₆ alkenyl group, or        -   (D.2) at least one organosilicon compound comprising at            least one epoxy radical, or        -   (D.3) at least one metal chelate M and/or a metal alkoxide            of general formula: M(OJ)n, with n=valency of M and J=linear            or branched C₁-C₈ alkyl,    -   M being chosen from the group formed by: Ti, Zr, Ge, Li, Mn, Fe,        Al and Mg or mixtures thereof.

In accordance with a preferred embodiment of the invention, thealkoxylated organosilane (D.1) of the adhesion promoter D is chosen fromthe products having the general formula below:

in which formula:

-   -   R1, R2 and R3 are hydrogenated radicals or identical or        different hydrocarbon-based radicals and represent a hydrogen        atom, a linear or branched C₁-C₄ alkyl or a phenyl optionally        substituted with at least one C₁-C₃ alkyl,    -   U is a linear or branched C₁-C₄ alkylene,    -   W is a valency bond,    -   R⁴ and R⁵ are identical or different radicals and represent a        linear or branched C₁-C₄ alkyl,    -   x′=0 or 1, and    -   x x=0 to 2.

Without this being limiting, it may be considered thatvinyltrimethoxysilane is a particularly suitable compound (D.1).

As regards the organosilicon compound (D.2), it is envisaged inaccordance with the invention to choose it:

-   -   a) either from the products (D.2a) corresponding to the        following general formula:

-   -   -   in which formula:        -   R⁶ is a linear or branched C₁-C₄ alkyl radical,        -   R⁷ is a linear or branched alkyl radical,        -   y is equal to 0, 1 or 3, and        -   X being defined by the following formula:

-   -   -   -   with:

        -   E and D which are identical or different radicals chosen            from linear or branched C₁-C₄ alkyls,

        -   z is equal to 0 or 1,

        -   R⁸, R⁹, R¹⁰ which are identical or different radicals            representing a hydrogen atom or a linear or branched C₁-C₄            alkyl, and

        -   R⁸ and R⁹ or R¹⁰ which may alternatively constitute,            together with the two carbons bearing the epoxy, a 5- to            7-membered alkyl ring, or

    -   b) or from the products (D.2b) formed by epoxy-functional        polydiorganosiloxanes comprising:        -   (i) at least one siloxyl unit having the formula:

$\begin{matrix}{X_{p}G_{q}{SiO}\frac{4 - \left( {p + q} \right)}{2}} & \left( {D{.2}\mspace{14mu} {bi}} \right)\end{matrix}$

-   -   -   -   in which formula:

        -   X is the radical as defined above for formula (D.2 a)

        -   G is a monovalent hydrocarbon-based group, free of an            unfavorable action on the activity of the catalyst, and            chosen from alkyl groups containing from 1 to 8 carbon atoms            inclusive, optionally substituted with at least one halogen            atom, and also from aryl groups containing between 6 and 12            carbon atoms,

        -   p=1 or 2,

        -   q=0, 1 or 2,

        -   p+q=1, 2 or 3, and

        -   (ii) optionally at least one siloxyl unit having the            formula:

$\begin{matrix}{G_{r}{SiO}\frac{4 - r}{2}} & \left( {D{.2}\mspace{14mu} {bii}} \right)\end{matrix}$

-   -   -   in which formula G has the same meaning as above and r is            equal to 0, 1, 2 or 3.

As regards the last compound (D.3) of the adhesion promoter D, thepreferred products are those in which the metal M of the chelate and/orof the alkoxide (D.3) is chosen from the following list: Ti, Zr, Ge, Lior Mn. It should be pointed out that titanium is more particularlypreferred. It may be combined, for example, with an alkoxy radical ofbutoxy type.

The adhesion promoter D may be formed from:

-   -   (D.1) alone    -   (D.2) alone    -   (D.1)+(D.2)

Or according to two preferred modes of:

-   -   (D.1)+(D.3)    -   (D.2)+(D.3)

and finally, according to the most preferred mode: (D.1)+(D.2)+(D.3).

According to the invention, an advantageous combination for forming theadhesion promoter is the following:

-   -   vinyltrimethoxysilane (VTMO), 3-glycidoxypropyltrimethoxysilane        (GLYMO) and butyl titanate.

In quantitative terms, it may be pointed out that the weight proportionsbetween (D.1), (D.2) and (D.3), expressed as weight percentages relativeto the total of the three, are as follows:

-   -   (D.1)≤10, preferably between 15 and 70 and even more        preferentially between 25 and 65,    -   (D.2)≤90, preferably between 70 and 15 and even more        preferentially between 65 and 25, and    -   (D.3)≤1, preferably between 5 and 25 and even more        preferentially between 8 and 18,

it being understood that the sum of these proportions of (D.1), (D.2)and (D.3) is equal to 100%.

For better adhesion properties, the weight ratio (D.2):(D.1) ispreferably between 2:1 and 0.5:1, the ratio 1:1 being more particularlypreferred.

Advantageously, the adhesion promoter D is present in a proportion offrom 0.1 to 10% by weight, preferably 0.5 to 5% by weight and morepreferentially from 1 to 3% by weight, relative to the total weight ofall of the constituents of the composition X.

According to a particular embodiment, the composition X according to theinvention also comprises at least one filler E.

The fillers E optionally contained in the compositions according to theinvention are preferably mineral. They may especially be siliceous. Whenthey are siliceous materials, they may act as reinforcing orsemi-reinforcing filler. The reinforcing siliceous fillers are chosenfrom colloidal silicas, powders of fumed silica and of precipitatedsilica, or a mixture thereof. These powders have a mean particle sizegenerally less than 0.1 μm (micrometers) and a BET specific surface areaof greater than 30 m²/g, preferably between 30 and 350 m²/g.Semi-reinforcing siliceous fillers such as diatomaceous earths or groundquartz may also be used. As regards the nonsiliceous mineral materials,they may be included as semi-reinforcing or bulking mineral filler.Examples of these nonsiliceous fillers that may be used, alone or as amixture, are carbon black, titanium dioxide, aluminum oxide, hydratedalumina, expanded vermiculite, non-expanded vermiculite, calciumcarbonate optionally surface-treated with fatty acids, zinc oxide, mica,talc, iron oxide, barium sulfate and slaked lime. These fillers have aparticle size generally between 0.001 and 300 μm (micrometers) and a BETsurface area of less than 100 m²/g. In practical but nonlimiting terms,the fillers used may be a mixture of quartz and silica. The fillers maybe treated with any suitable product. In terms of weight, use ispreferably made of an amount of filler of between 1% and 50% andpreferably between 1% and 40% by weight relative to all the constituentsof the composition.

The composition X according to the invention may also comprise one ormore common functional additives. Families of common functionaladditives that may be mentioned include:

-   -   silicone resins,    -   adhesion modifiers,    -   consistency-enhancing additives,    -   pigments, and    -   heat-resistance, oil-resistance or fire-resistance additives,        for example metal oxides.

Silicone resins are branched organopolysiloxane oligomers or polymersthat are well known and commercially available. They have, in theirstructure, at least two different units chosen from those of formulaR₃SiO_(1/2) (M unit), R₂SiO_(2/2) (D unit), RSiO_(3/2) (T unit) andSiO_(4/2) (Q unit) with at least one of these units being a T or Q unit.

The radicals R are identical or different and are chosen from linear orbranched C1-C6 alkyl, hydroxyl, phenyl or 3,3,3-trifluoropropylradicals. Examples of alkyl radicals that may be mentioned includemethyl, ethyl, isopropyl, tert-butyl and n-hexyl radicals.

Examples of branched organopolysiloxane oligomers or polymers that maybe mentioned include MQ resins, MDQ resins, TD resins and MDT resins, itbeing possible for the hydroxyl functions to be borne by the M, D and/orT units. As examples of resins that are particularly suitable for use,mention may be made of hydroxylated MDQ resins with a weight content ofhydroxyl groups of between 0.2 and 10% by weight.

The compositions X according to the invention may especially be obtainedby first introducing the catalyst C into the reaction medium, followedby adding the organopolysiloxane A with stirring. Finally, theorganohydrogenopolysiloxane compound B is introduced and the temperatureof the mixture is increased to reach the crosslinking temperature. Themixture is maintained at the crosslinking temperature until the stirringstops due to an increase in the viscosity of the mixture.

A subject of the present invention is also a process for crosslinkingsilicone compositions, characterized in that it consists in heatingcomposition X as defined previously to a temperature ranging from 70 to200° C., preferably from 80 to 150° C. and more preferentially from 80to 130° C.

A subject of the invention is also a crosslinked silicone material Yobtained by heating to a temperature ranging from 70 to 200° C.,preferably from 80 to 150° C. and more preferentially from 80 to 130°C., of a crosslinkable composition X comprising:

-   -   at least one organopolysiloxane compound A comprising, per        molecule, at least two C₂-C₆ alkenyl radicals bonded to silicon        atoms,    -   at least one organohydrogenopolysiloxane compound B comprising,        per molecule, at least two hydrogen atoms bonded to an identical        or different silicon atom,    -   at least one catalyst C which is a complex corresponding to the        following formula:

[Fe(L¹)₂]

in which:

-   -   the symbol Fe represents iron in oxidation state II,    -   the symbols L¹, which may be identical or different, represent a        ligand which is a β-dicarbonylato anion or the enolate anion of        a β-dicarbonyl compound,    -   optionally at least one adhesion promoter D and    -   optionally at least one filler E.

The composition according to the invention has the advantage of notbeing air-sensitive and thus of being able to be used and especiallycrosslinked under a non-inert atmosphere, and in particular in air.

The present invention is illustrated in greater detail in the followingnonlimiting implementation example.

EXAMPLE: IRON-BASED CATALYSTS FOR THE CROSSLINKING OF M^(vi) D₇₀ M^(vi)WITH MD′₅₀M I) Constituents

1) Organopolysiloxane A of formula M^(vi)D₇₀M^(vi) (0.038 mol of vinylradicals bonded to silicon per 100 g of oil), with: Vi=Vinyl; M^(vi):(CH₃)₂ViSiO_(1/2) and D: (CH₃)₂SiO_(2/2)2) Organohydrogenopolysiloxane B of formula: MD′₅₀M (1.58 mol ofhydrogen atoms bonded to silicon per 100 g of oil), with: M:(CH₃)₃SiO_(1/2); and D′: (CH₃)HSiO_(2/2)

3) Catalysts (A) and (B)

The catalysts (A) and (B) are obtained via a synthesis that is wellknown to those skilled in the art:

The acac or THMD compound (supplier: Strem) is, in a first stage,deprotonated using one equivalent of Bu-Li (supplier: Sigma-Aldrich) atlow temperature (−78° C.). The salt obtained is recrystallized fromdiethyl ether. The deprotonated ligand obtained (lithium salt) is addedto an iron chloride (FeCl₂) dissolved in THF at room temperature (12hours). After separation of the phases by settling, filtration andconcentration, the complex is recrystallized from THF.

The complex [Fe(acac)₂] is in the form of an orangey brown solid.

The complex [Fe(THMD)₂] is in the form of an oily bright red solid.

II) Formulations and Results:

For each formulation tested, the catalyst is weighed and introduced atroom temperature into a glass flask.5 g of oil M^(vi)D₇₀M^(vi) are then introduced, followed by 0.6 g of oilMD′₅₀M.The flask is stirred in an oil bath which will be heated to the desiredreaction temperature.The ratio R corresponding to the mole ratio of hydrogen atoms bonded tosilicon (Si—H) in the organohydrogenopolysiloxane (MD′₅₀M) to thealkenyl radicals (in this instance vinyl) bonded to silicon (Si—CH═CH₂)in the organopolysiloxane (dvtms) being 4:1.The start of crosslinking is measured. The start of crosslinking isdefined as being the stopping of stirring due to an increase in theviscosity of the medium.

TABLE 1 Reaction mol % of Start of Catalyst temperature catalyst⁽¹⁾Ratio R Atmosphere crosslinking Formulation 1 [Fe(acac)₂] 200° C. 2% 4:1Not inert Between (invention) 6 h and 20 h Formulation 2 [Fe(TMHD)₂]200° C. 2% 4:1 Not inert 24 h (invention) ⁽¹⁾Expressed as mol % of ironper number of moles of vinyl radicals bonded to silicon (Si—CH═CH₂) indvtms

The results show that the formulations 1 and 2 according to theinvention, in which the catalyst is a Fe(II) complex bearingtwo-dicarbonyl ligands, crosslink between 6 h and 24 h.

1- A crosslinkable composition X comprising: at least oneorganopolysiloxane compound A comprising, per molecule, at least twoC₂-C₆ alkenyl radicals bonded to silicon atoms, at least oneorganohydrogenopolysiloxane compound B comprising, per molecule, atleast two hydrogen atoms bonded to an identical or different siliconatom, at least one catalyst C which is a complex corresponding to thefollowing formula:[Fe(L¹)₂] in which: the symbol Fe represents iron in oxidation state II,the symbols L¹, which may be identical or different, represent a ligandwhich is a β-dicarbonylato anion or the enolate anion of a β-dicarbonylcompound, optionally at least one adhesion promoter D and optionally atleast one filler E. 2- The composition X as claimed in claim 1, whereinthe catalyst C is present in a content ranging from 0.001 to 10 mol % ofiron per number of moles of C₂-C₆ alkenyl radicals bonded to siliconatoms in the organopolysiloxane compound A, optionally from 0.01 to 7%,and optionally from 0.1 to 5%. 3- The composition X claimed in claim 1,wherein said composition is free of catalyst based on platinum,palladium, ruthenium or rhodium. 4- The composition X as claimed inclaim 1, wherein the ligand L¹ is an anion derived from a compound offormula (1):R¹COCHR²COR³  (1) in which: R¹ and R³, which may be identical ordifferent, represent a linear, cyclic or branched C₁-C₃₀hydrocarbon-based radical, an aryl containing between 6 and 12 carbonatoms or a radical —OR⁴ with R⁴ representing a linear, cyclic orbranched C₁-C₃₀ hydrocarbon-based radical, R² is a hydrogen atom or ahydrocarbon-based radical, optionally an alkyl radical comprising from 1to 4 carbon atoms; with R¹ and R² may be joined together to form a C₅-C₆ring, and R² and R⁴ may be joined together to form a C₅-C₆ ring. 5- Thecomposition X as claimed in claim 1, in which the compound of formula(1) is chosen from the group formed by the following β-diketones:2,4-pentanedione (acac); 2,4-hexanedione; 2,4-heptanedione;3,5-heptanedione; 3-ethyl-2,4-pentanedione; 5-methyl-2,4-hexanedione;2,4-octanedione; 3,5-octanedione; 5,5-dimethyl-2,4-hexanedione;6-methyl-2,4-heptanedione; 2,2-dimethyl-3,5-nonanedione;2,6-dimethyl-3,5-heptanedione; 2-acetylcyclohexanone (Cy-acac);2,2,6,6-tetramethyl-3,5-heptanedione (TMHD);1,1,1,5,5,5-hexafluoro-2,4-pentanedione (F-acac); benzoylacetone;dibenzoylmethane; 3-methyl-2,4-pentadione; 3-acetyl-2-pentanone;3-acetyl-2-hexanone; 3-acetyl-2-heptanone; 3-acetyl-5-methyl-2-hexanone;benzoylstearoylmethane; benzoylpalmitoylmethane; octanoylbenzoylmethane;4-t-butyl-4′-methoxydibenzoylmethane; 4,4′-dimethoxydibenzoylmethane and4,4′-di-tert-butyldibenzoylmethane, and optionally from the β-diketones2,4-pentanedione (acac) and 2,2,6,6-tetramethyl-3,5-heptanedione (TMHD).6- The composition X as claimed in claim 1, in which the catalyst C ischosen from the complexes [Fe(acac)₂] and [Fe(TMHD)_(2]). 7- Thecomposition X as claimed in claim 1, wherein the organopolysiloxane Acomprises: (i) at least two siloxyl units (A.1), which may be identicalor different, having the following formula: $\begin{matrix}{W_{a}Z_{b}{SiO}_{\frac{4 - {({a + b})}}{2}}} & \left( {A{.1}} \right)\end{matrix}$ in which: a=1 or 2, b=0, 1 or 2 and a+b=1, 2 or 3; thesymbols W, which may be identical or different, represent a linear orbranched C₂-C₆ alkenyl group, and the symbols Z, which may be identicalor different, represent a monovalent hydrocarbon-based group containingfrom 1 to 30 carbon atoms, optionally chosen from the group formed byalkyl groups containing from 1 to 8 carbon atoms and aryl groupscontaining between 6 and 12 carbon atoms, and optionally chosen from thegroup formed by methyl, ethyl, propyl, 3,3,3-trifluoropropyl, xylyl,tolyl and phenyl radicals, (ii) and optionally at least one siloxyl unithaving the following formula: $\begin{matrix}{Z_{a}^{1}{SiO}_{\frac{4 - a}{2}}} & \left( {A{.2}} \right)\end{matrix}$ in which: a=0, 1, 2 or 3, the symbols Z¹, which may beidentical or different, represent a monovalent hydrocarbon-based groupcontaining from 1 to 30 carbon atoms, optionally chosen from the groupformed by alkyl groups containing from 1 to 8 carbon atoms inclusive andaryl groups containing between 6 and 12 carbon atoms, and optionallychosen from the group formed by methyl, ethyl, propyl,3,3,3-trifluoropropyl, xylyl, tolyl and phenyl radicals. 8- Thecomposition X as claimed in claim 1, in which theorganohydrogenopolysiloxane compound B comprises at least three hydrogenatoms per molecule directly bonded to an identical or different siliconatom. 9- The composition X as claimed in claim 1, in which theorganohydrogenopolysiloxane compound B is an organopolysiloxanecomprising: (i) at least two siloxyl units and optionally at least threesiloxyl units having the following formula: $\begin{matrix}{H_{d}Z_{e}^{3}{SiO}_{\frac{4 - {({d + e})}}{2}}} & \left( {B{.1}} \right)\end{matrix}$ in which: d=1 or 2, e=0, 1 or 2 and d+e=1, 2 or 3, thesymbols Z³, which may be identical or different, represent a monovalenthydrocarbon-based group containing from 1 to 30 carbon atoms, optionallychosen from the group formed by alkyl groups containing from 1 to 8carbon atoms and aryl groups containing between 6 and 12 carbon atoms,and optionally chosen from the group formed by methyl, ethyl, propyl,3,3,3-trifluoropropyl, xylyl, tolyl and phenyl radicals, and (ii)optionally at least one siloxyl unit having the following formula:$\begin{matrix}{Z_{c}^{2}{SiO}_{\frac{4 - c}{2}}} & \left( {B{.2}} \right)\end{matrix}$ in which: c=0, 1, 2 or 3, the symbols Z², which may beidentical or different, represent a monovalent hydrocarbon-based groupcontaining from 1 to 30 carbon atoms, optionally chosen from the groupformed by alkyl groups containing from 1 to 8 carbon atoms and arylgroups containing between 6 and 12 carbon atoms, and even morepreferentially chosen from the group formed by methyl, ethyl, propyl,3,3,3-trifluoropropyl, xylyl, tolyl and phenyl radicals. 10- Thecomposition X as claimed in claim 1, wherein said composition comprisesa second organopolysiloxane compound comprising, per molecule, at leasttwo C₂-C₆ alkenyl radicals bonded to silicon atoms, different from theorganopolysiloxane compound A, said second organopolysiloxane compoundoptionally being divinyltetramethyl siloxane. 11- The composition X asclaimed in claim 1, wherein proportions of the organopolysiloxane A andof the organohydrogenopolysiloxane B are such that the mole ratio ofhydrogen atoms bonded to silicon in the organohydrogenopolysiloxane B tothe alkenyl radicals bonded to silicon in the organopolysiloxane A isbetween 0.2 and 20, optionally between 0.5 and 15, optionally between0.5 and 10 and optionally between 0.5 and
 5. 12- The composition X asclaimed in claim 1, wherein said composition comprises one or morefunctional additives chosen from: silicone resins, adhesion modifiers,consistency-enhancing additives, pigments, and heat-resistance,oil-resistance or fire-resistance additives, optionally metal oxides.13- A product comprising a catalyst C, which is a complex correspondingto the following formula:[Fe(L¹)₂] in which: the symbol Fe represents iron in oxidation state II,the symbols L¹, which may be identical or different, represent a ligandwhich is a β-dicarbonylato anion or the enolate anion of a β-dicarbonylcompound as a catalyst for crosslinking of one or more siliconecompositions. 14- A process for crosslinking one or more siliconecompositions, wherein said process comprises heating a composition X asclaimed in claim 1 to a temperature ranging from 70 to 200° C.,optionally from 80 to 150° C. and optionally from 80 to 130° C. 15- Acrosslinked silicone material Y obtained by heating to a temperatureranging from 70 to 200° C., optionally from 80 to 150° C. and optionallyfrom 80 to 130° C., a composition X as claimed in claim 1.